Remotely configurable add/drop for wavelength division multiplexing and method of operating the same

ABSTRACT

Novel architectures of integrated optical add/drop wavelength division multiplexers and FTIR switches are disclosed. In one embodiment, an add/drop includes: (1) a primary refracting body having a total internal reflecting surface and capable of transmitting optical energy therethrough, (2) a frustrating refracting body having a frustrating surface located proximate the total internal reflecting surface, (3) an actuator, coupled to the primary refracting body and the frustrating refracting body, that drives the frustrating refracting body thereby to frustrate a reflection of the total internal reflecting surface and (4) an optical filter, optically aligned with the primary refracting body, that configurably passes selected wavelengths of light through the primary refracting body and reflects remaining wavelengths.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] The present application is a continuation-in-part of U.S. patentapplication Ser. No. 09/826,455, filed on Apr. 5, 2001 by Laughlin,entitled “Total Internal Reflection Optical Switch and Method ofOperating the Same” and incorporated herein by reference.

TECHNICAL FIELD OF THE INVENTION

[0002] The present invention is directed, in general, to opticalswitches and, more specifically, to a remotely configurable add/drop forwavelength division multiplexing (WDM) and a method of operating thesame.

BACKGROUND OF THE INVENTION

[0003] In today's rapidly expanding wavelength division multiplexingoptical network, a critical need exists for a simple, low cost,reconfigurable wavelength division multiplexer having an add/dropcapability (often referred to simply as an “add/drop”). Add/drops finduse in a network having a number of communication nodes where one ormore wavelengths may require temporarily added and or dropped at aspecific node. To achieve this adding and dropping, the optical fibersinterconnecting the network must be remotely configurable to add anddrop the wavelengths as required.

[0004] Currently, several different technologies are used to providewavelength division multiplexing and the adding and dropping ofindividual wavelengths. The earliest wavelength division multiplexingtechnology used hardwired adds and drops. These adds and drops werepermanent; they always added or dropped the same specific wavelengths ata given node. This had the drawback of not being remotely configurable.

[0005] The newer techniques for remotely configurable add and dropwavelength division multiplexing first demultiplex the individualwavelengths in the beam and then re-multiplex the individual wavelengthsinto a combined signal. One or more discrete switches are then insertedin the demultiplexed signal to add and drop wavelengths. This has thedrawback of being complex and requiring redundant components.

[0006] What is needed in the art is a remotely reconfigurable add/drop.What is further needed in the art is a method of operating such add/dropto add and/or drop particular wavelengths of light on command.

SUMMARY OF THE INVENTION

[0007] The present invention takes advantage of a frustrated totalinternal reflection (FTIR) optical switch included in the subject matterof the patent application incorporated herein by reference. It has beendiscovered that the FTIR switch can be augmented with an optical filterto effect reconfigurable WDM and thereby a wavelength-dependent add/dropfunction.

[0008] Accordingly, the present invention provides novel architecturesof integrated optical add/drop wavelength division multiplexers and FTIRswitches. In one embodiment, an add/drop includes: (1) a primaryrefracting body having a total internal reflecting surface and capableof transmitting optical energy therethrough, (2) a frustratingrefracting body having a frustrating surface located proximate the totalinternal reflecting surface, (3) an actuator, coupled to the primaryrefracting body and the frustrating refracting body, that drives thefrustrating refracting body thereby to frustrate a reflection of thetotal internal reflecting surface and (4) an optical filter, opticallyaligned with the primary refracting body, that configurably passesselected wavelengths of light through the primary refracting body andreflects remaining wavelengths.

[0009] In one embodiment of the present invention, the light encountersthe optical filter before the frustrating refracting body (meaning thatthe optical filter is opposite the add/drop from the add/drop fibers).In an alternative embodiment, the light encounters the optical filterafter the frustrating refracting body (meaning that the optical filteris adjacent the add/drop fibers). Though either alternative is possible,the former is slightly preferable, in that losses may be held to below 1decibel for wavelengths passing through the add/drop.

[0010] In one embodiment of the present invention, the optical filter isactually coupled to the main refracting body. In another embodiment, theoptical filter is composed of a dielectric material. Those skilled inthe art will understand, however, that any appropriate material may beemployed to construct a suitable bandpass, comb, shortpass or longpassfilter, depending upon the desired filter function.

[0011] In one embodiment of the present invention, the primaryrefracting body is composed of glass. Those skilled in the pertinent artwill realize, however, that the primary refracting body can be composedof any appropriate transparent material.

[0012] In one embodiment of the present invention, the frustratingrefracting body is composed of glass. Those skilled in the pertinent artwill realize, however, that the frustrating refracting body can becomposed of any appropriate transparent material.

[0013] In one embodiment of the present invention, the actuator iscomposed of a piezoelectric bimorph. Alternatively, the actuator may bea mechanical structure of suitable speed and precision.

[0014] In one embodiment of the present invention, the add/drop furtherincludes: (1) a first collimating lens optically aligned with theoptical filter and (2) a first input fiber and a first output fibercoupled to the first collimating lens. In an embodiment to beillustrated and described, the add/drop further includes: (1) a firstcollimating lens optically aligned with the optical filter, (2) a secondcollimating lens coupled to a surface of the main refractive body, (3) afirst input fiber and a first output fiber coupled to the firstcollimating lens and (4) a second input fiber and a second output fibercoupled to the second collimating lens.

[0015] In alternative embodiments of the present invention, the actuatordrives the frustrating refracting body from the open state to the closedstate or from the closed state to the open state. Thus, the add/drop maybe normally open or normally closed. In the embodiment to be illustratedand described, the add/drop is normally open and driven closed.

[0016] The foregoing has outlined, rather broadly, preferred andalternative features of the present invention so that those skilled inthe art may better understand the detailed description of the inventionthat follows. Additional features of the invention will be describedhereinafter that form the subject of the claims of the invention. Thoseskilled in the art should appreciate that they can readily use thedisclosed conception and specific embodiment as a basis for designing ormodifying other structures for carrying out the same purposes of thepresent invention. Those skilled in the art should also realize thatsuch equivalent constructions do not depart from the spirit and scope ofthe invention in its broadest form.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] For a more complete understanding of the present invention,reference is now made to the following descriptions taken in conjunctionwith the accompanying drawings, in which:

[0018]FIG. 1 illustrates an optical schematic of a prior art apparatushaving a collimated beam from a lens reflected back upon itself;

[0019]FIG. 2 illustrates an optical schematic of a prior art apparatushaving a pair of fibers connected to a second pair of fibers with twocollimating lenses;

[0020]FIG. 3 illustrates a TIR optical switch constructed according tothe principles of the present invention;

[0021]FIG. 4 illustrates a graphical representation of reflection andtransmission at a TIR interface constructed according to the principlesof the present invention as a function of spacing;

[0022]FIGS. 5A and 5B together illustrate optical schematics of the TIRreversing switch of FIGS. 3 and 7;

[0023]FIG. 6 illustrates an N×N cross bar switch composed of multipleTIR reversing switches and constructed according to the principles ofthe present invention;

[0024]FIG. 7 illustrates a TIR reversing optical switch constructedaccording to the principles of the present invention;

[0025]FIG. 8 illustrates an optical schematic of a prior art apparatushaving two collimating lens with an optical filter inserted between todrop and add a single wavelength or group of wavelengths;

[0026]FIG. 9 illustrates an optical schematic of a prior art apparatushaving multiple filters inserted between multiple collimating lens todrop multiple wavelengths;

[0027]FIG. 10 illustrates filter integrated with an FTIR optical switch,resulting in a remotely configurable add/drop constructed according tothe principles of the present invention;

[0028]FIG. 11 illustrates multiple filters integrated with multiple FTIRswitches, resulting in an integrated channel add/drop multiplexerconstructed according to the principles of the present invention; and

[0029]FIG. 12 illustrates multiple add/drops cascaded for adding anddropping multiple wavelengths constructed according to the principles ofthe present invention.

DETAILED DESCRIPTION

[0030] Referring initially to FIG. 1, illustrated is an opticalschematic of a prior art apparatus having a collimated beam from a lensreflected back upon itself. FIG. 1 is presented for the purpose ofconveying basic optical principles of which the illustrated embodimentof the present invention takes advantage.

[0031] A first input fiber 12 provides a source of optical energy andterminates at a focal plane of a first collimating lens 16 thatcollimates the optical energy emanating from the first input fiber intoa collimated beam 17. The first collimating lens 16 is illustrated asbeing a gradient index of refraction (GRIN) lens.

[0032] The collimated beam 17 impinges upon and is reflected from amirror 18 at mutually dependent angles and returned to the firstcollimating lens 16. The first collimating lens 16 focuses the opticalenergy onto a first output fiber 20 terminating at the focal plane ofthe first collimating lens 16. The first output fiber 20 serves as areceptor for the optical energy. By this process, the optical energy hasbeen transferred from the first input fiber 12 to the first output fiber20.

[0033] Turning now to FIG. 2, illustrated is an optical schematic of aprior art apparatus having a pair of fibers connected to a second pairof fibers with two collimating lenses. Like FIG. 1, FIG. 2 is presentedfor the purpose of conveying basic optical principles of which theillustrated embodiment of the present invention takes advantage.

[0034]FIG. 2 shows the first input fiber 12, again providing a source ofoptical energy and terminating at the focal plane of the collimatinglens 16. As before, the collimating lens 16 collimates the opticalenergy emanating from the first input fiber 12 into the collimated beam17. However, in contrast to FIG. 1, the collimated beam 17 is projectedinstead into a second collimating lens 22. The second collimating lens22 focuses the collimated beam 17 onto a second output fiber 26 thatterminates at a focal plane of the second collimating lens 22. Thesecond output fiber 26 serves as a receptor for the optical energy. Bythis process, the optical energy has been transferred from the firstinput fiber 12 to the second output fiber 26.

[0035] Opposing optical energy is introduced at a second input fiber 24terminating at the focal plane of the second collimating lens 22. Thesecond collimating lens 22 collimates the optical energy emanating fromthe second input fiber 24 into a beam 28. The collimated beam 28 isprojected into the first collimating lens 16, which, in turn, focusesthe energy onto the first output fiber 20. The first output fiber 20serves as a receptor for the optical energy. By this process, theoptical energy has been transferred from the second input fiber 24 tothe first output fiber 20.

[0036] Turning now to FIG. 3, illustrated is a TIR optical switch,generally designated 32, constructed according to the principles of thepresent invention. The TIR optical switch 32 has a first spacer 48 and asecond spacer 36 that cooperate to separate an actuator 46 from afrustrating refracting body 44. It is advantageous (and in theillustrated embodiment, important) that the first spacer 48 haveessentially the same coefficient of expansion as the second spacer 36.

[0037] In the illustrated embodiment, the first and second spacers 48,36are composed of glass or ceramic. The actuator 46 in the illustratedembodiment is a piezoelectric bimorph.

[0038] When an electrical impulse voltage is applied to the actuator 46,a center portion (not separately referenced, but adjoining the secondspacer 36) of the actuator 46 is deflected toward the primary refractingbody 44. In the preferred embodiment, the electrical impulse has a rapidrise time (less than 20 microseconds).

[0039] Deflection of the center portion of the actuator 46 may generatea shock wave (not shown) that travels through the second spacer 36 anddrives a frustrating refracting body 40 toward the primary refractingbody 44. If generated, the shock wave propagates through the frustratingrefracting body 40, causing a frustrating surface 42 of the frustratingrefracting body 40 to move from an initial position greater than onewavelength from a first total internal reflecting surface 33 of theprimary refracting body 44 to a subsequent position less than {fraction(1/10)}^(th) of a wavelength from the first total internal reflectingsurface 33.

[0040] By driving the frustrating refracting body 40 from its center, asopposed to its edge, the shock wave reaches the center of thefrustrating refracting body 40 before, or at essentially the same timeas, it reaches the edge of the frustrating refracting body 40. Thisorderly, outward progression of the shock wave essentially eliminatesthe indentation in the center of the frustrating refracting body 40which, in the past, caused a transient deformation 35 at the center ofthe frustrating refracting body 40. Minimization or absence of thetransient deformation minimizes or eliminates transient opticalreflection after closing.

[0041] It is recognized that many different mechanical arrangementsexist to facilitate the shock wave arriving at the center, and thus themotion first occurring at the center of the frustrating surface 42 ofthe frustrating refracting body 40 prior to reaching the edges of thefrustrating surface 42 of the frustrating refracting body 40.

[0042] It should be noted that, in alternative embodiments, the actuator46 drives the frustrating refracting body 40: (1) uniformly, at leastsubstantially reducing any shock wave that may form or (2) at a lowervelocity, again reducing or eliminating any shock waves. Thus, a shockwave is initiated only in the illustrated embodiment, and not in allembodiments of the present invention. Those skilled in the pertinent artwill further recognize that many different mechanical arrangements existto drive the frustrating refracting body 40 uniformly or at a lowervelocity.

[0043] The body of the frustrating refracting body 40 is transparent,such that light can travel through it. A mirror 41 is located within thefrustrating refracting body 40. The mirror 41 is formed of two flatmirror surfaces oriented essentially normal to the direction of theoptical axes of the first and second collimating lenses 16, 22. In theillustrated embodiment, the mirror 41 is composed of enhanced silver,although those skilled in the pertinent art will realize that othermaterials fall within the broad scope of the present invention.

[0044] Turning now to FIG. 4, illustrated is a graphical representationof reflection and transmission at a TIR interface constructed accordingto the principles of the present invention as a function of spacing.Shown are curves corresponding to: (1) transmission of optical energy inthe plane of incidence Tp (curve 52), (2) transmission of optical energyperpendicular to the plane of incidence Ts (curve 54), (3) reflection ofoptical energy in the plane of incidence Rp (curve 56) and (4)reflection of optical energy perpendicular to the plane of incidence Rs(curve 58).

[0045]FIG. 4 well illustrates how an air gap of {fraction (1/10)}^(th)of a wavelength or less yields substantial transmission and negligiblereflection and how an air gap of more than a full wavelength yieldsnegligible transmission and substantial reflection. FIG. 4 alsoillustrates an intermediate region 53 in which transmission andreflection occur more or less concurrently. The optical switch of thepresent invention can be driven to operate in this region as well,allowing multiple output light beams (of controllable relativeintensity, no less) to be selectively spawned from a single input lightbeam.

[0046] Turning concurrently now to FIGS. 5A and 5B, illustrated areoptical schematics of the TIR reversing switch 32 of FIG. 3. The switchis illustrated in two configurations as a switch 61 and a switch 63,respectively.

[0047] Regarding FIG. 5A, optical energy is initially routed from thefirst input fiber 12 to the first output fiber 26. Optical energy isalso initially routed from the opposing second fiber input 24 to thesecond fiber output 20. Upon actuation, optical energy is reversed, andinstead routed from the first fiber input 12 to the second output fiber20. Likewise, optical energy is instead routed from the second inputfiber 24 to the first fiber output 26. The common name for this TIRreversing switch 61 is a 2×2 reversing bypass switch 61.

[0048]FIG. 5B illustrates the same switch, made to function as a 2×2cross bar switch 63. Optical energy is initially routed from the firstinput fiber 12 to the first output fiber 26. Optical energy is alsoinitially routed from the second input fiber 24 to the second outputfiber 20. Upon actuation, optical energy is reversed and instead routedfrom the first fiber input 12 to the second output fiber 20. Likewise,optical energy is instead routed from the second input fiber 24 to thesecond fiber output 26.

[0049] Turning now to FIG. 6, illustrated is an N×N (specifically a 4×4)cross bar switch composed of multiple TIR reversing optical switches andconstructed according to the principles of the present invention. FIG. 6shows six TIR reversing optical switches (not separately referenced)configured as 2×2 cross bar switches to yield a 4×4 cross bar switch,generally referenced as 64. Each of several input fibers 12, 24, 66, 68can be connected to any of several output fibers 70, 72, 74, 76. It isapparent that greater numbers of TIR reversing optical switches can becascaded in like manner to form an optical switch of arbitrarily large(N×N) size.

[0050]FIG. 7 illustrates a TIR reversing optical switch, generallyreferenced as 50, constructed according to the principles of the presentinvention. FIG. 7 will be initially described assuming that the TIRreversing switch 50 is in an open state, the air gap 35 being perhaps onthe order of one and a half wavelengths in thickness.

[0051] The first input fiber 12 provides a source of optical energy andterminates at the focal plane of the collimating lens 16. Thecollimating lens 16 collimates the optical energy emanating from thefirst input fiber 12 into a beam 17. By virtue of the physicalphenomenon of total internal reflection, the collimated beam 17 isreflected off of the first total internal reflecting surface into asecond collimating lens 22. The second collimating lens 22 focuses thecollimated beam 17 onto a second output fiber 26 that terminates at afocal plane of the second collimating lens 22. The second output fiber26 serves as a receptor for the optical energy. By this process, theoptical energy has been transferred from the first input fiber 12 to thesecond output fiber 26.

[0052] Opposing optical energy is introduced at a second input fiber 24terminating at the focal plane of the second collimating lens 22. Thesecond collimating lens collimates the optical energy emanating from thesecond input fiber 24 into a beam 28. The collimated beam 28 isreflected off of the first total internal reflecting surface 33 into thefirst collimating lens 16, which, in turn, focuses the energy onto thefirst output fiber 20. The first output fiber 20 serves as a receptorfor the optical energy. By this process, the optical energy has beentransferred from the second input fiber 24 to the first output fiber 20.

[0053] Now FIG. 7 will be described assuming that the TIR reversingswitch 50 is in a closed state, the air gap 35 being perhaps less than{fraction (1/10)}^(th) of a wavelength in thickness. The first inputfiber 12 provides a source of optical energy and terminates at the focalplane of the first collimating lens 16 that collimates the opticalenergy emanating from the first input fiber 12 into a beam 17.

[0054] The air gap 35 having substantially closed and the reflection ofthe first total internal reflecting surface 33 having been frustrated,the collimated beam 17 passes through the interface defined by the firsttotal internal reflecting surface 33 and the frustrating surface 42 ofthe frustrating refracting body 40. The collimated beam 17 then impingesupon and is reflected from a mirror 38 formed on or proximate thefrustrating refracting body 40 (though not shown, the mirror 38 may bestood-off from a backside of the frustrating refracting body 40 withoutmaterially changing the beam-reversing function of the mirror 38). Thecollimated beam 17 then passes back through the interface defined by thefirst total internal reflecting surface 33 and the frustrating surface42 and returns to the first collimating lens 16. The first collimatinglens 16 focuses the optical energy onto the first output fiber 20. Bythis process, the optical energy has been transferred from the firstinput fiber 12 to the first output fiber 20.

[0055] In like fashion, the second input fiber 12 provides an opposingsource of optical energy and terminates at the focal plane of the secondcollimating lens 22 that collimates the optical energy emanating fromthe second input fiber 24 into a collimated beam 28.

[0056] The air gap 35 again having substantially closed and thereflection of the first total internal reflecting surface 33 frustrated,the collimated beam 28 passes through the interface defined by the firsttotal internal reflecting surface 33 and the frustrating surface 42 ofthe frustrating refracting body 40. The collimated beam 28 then impingesupon and is reflected from the mirror 38. The collimated beam 28 thenpasses back through the interface defined by the first total internalreflecting surface 33 and the frustrating surface 42 and returns to thesecond collimating lens 22. The first collimating lens 22 focuses theoptical energy onto the second output fiber 26. By this process, theoptical energy has been transferred from the second input fiber 24 tothe second output fiber 26.

[0057] Turning now to FIG. 8, illustrated is an optical schematic of aprior art apparatus having two collimating lens with an optical filterinserted between to drop and add a single wavelength or group ofwavelengths. FIG. 8 is presented for the purpose of conveying basicoptical principles of which the illustrated embodiment of the presentinvention takes advantage and can be found as FIG. 10.11 on page 381 ofW. J. Tomlinson, “Optical Fiber Telecommunication II.”

[0058] A first input fiber 12 provides a source of multiple wavelengthoptical energy and terminates at a focal plane of a first collimatinglens 16 that collimates the optical energy emanating from the firstinput fiber into a collimated beam 17. The first collimating lens 16 isillustrated as being a GRIN lens.

[0059] The collimated beam 17 impinges upon an optical filter 101, thatis predominantly reflective at some wavelengths and predominantlytransmissive at one or more wavelengths. Some of the wavelengths, λ₁ . .. λ_(n)-λ_(m), of the collimated beam 17, are reflected at the filter101 at mutually dependent angles and returned to the first collimatinglens 16. The first collimating lens 16 focuses the optical energy λ₁ . .. λ_(n)-λ_(m) onto a first output fiber 26 terminating at the focalplane of the first collimating lens 16. At the same time λ_(m) istransmitted through the filter 101 and is focused by the lens 22 intothe first output fiber 20. This effectively drops λ_(m).

[0060] λ_(m)′ the add wavelength, is inserted at an add fiber 24 andcollimated by a lens 22. The collimated beam 28 of λ_(m)′ is transmittedto the output fiber 20. Any other wavelengths from the add fiber 24 arereflected by the filter 101 to the fiber 26. By this process, λ_(m) hasbeen separated from λ₁ . . . λ_(n) and dropped and λ_(m)′ has been addedto λ₁ . . . λ_(n) at the output fiber 20.

[0061] Turning now to FIG. 9, illustrated is an optical schematic of aprior art apparatus having four filters inserted between multiplecollimating lens to drop four wavelengths and can be found as FIG. 10.14on page 384 of “Optical Fiber Telecommunication II.” As FIG. 8, FIG. 9is presented for the purpose of conveying basic optical principles ofwhich the illustrated embodiment of the present invention takesadvantage.

[0062]FIG. 9 shows the first input fiber 12, again providing a source ofoptical energy with multiple wavelengths λ₁ . . . λ_(n) and terminatingat the focal plane of the collimating lens 16. As before, thecollimating lens 16 collimates the optical energy emanating from thefirst input fiber 12 into the collimated beam 17 and projects it onto anoptical filter 101 b. However, in contrast to FIG. 8, the collimatedbeam 17 is reflected onto filters 101 c, 101 d, 101 e. As in FIG. 8,λ_(b) is transmitted into a lens 22 b and focused onto and dropped at afiber 26 b. λ ₁ . . . λ_(n)-λ_(b) is then reflected to an optical filter101 c, where λ_(c) is transmitted into a lens 22 c and focused onto anddropped at a fiber 26 c. λ ₁ . . . λ_(n)-λ_(b)-λ_(c) is then reflectedto an optical filter 101 d, where λ_(d) is transmitted into a lens 22 dand focused onto and dropped at a fiber 26 d. λ ₁ . . .λ_(n)-λ_(b)-λ_(c)-λ_(d) is then reflected to an optical filter 101 e,where λ_(e) is transmitted into a lens 22 e and focused onto and droppedat a fiber 26 e. One skilled in the pertinent art would find it apparentthat the collimated beam 17 can be cascaded to any number of filters.Furthermore, these filters 101 b, 101 c, 101 d, 101 e, can be bandpass,comb, longpass or shortpass filters.

[0063] Turning now to FIG. 10, illustrated is a single channelintegrated optical add/drop multiplexer generally designated 120 andconstructed according to the principles of the present invention. Thesingle channel integrated optical add/drop multiplexer 120 introduces anoptical filter 101 between the collimating lens 16 the first refractingelement 44 of an FTIR reversing optical switch 50 as described in theapplication of which this is a continuation-in-part.

[0064]FIG. 10 will be initially described assuming that the FTIRreversing switch 50 is in an open state, the air gap 35 being perhaps onthe order of one wavelength in thickness. The first input fiber 12provides a source of optical energy containing multiple wavelengths λ₁ .. . λ_(n) and terminates at the focal plane of the collimating lens 16.The collimating lens 16 collimates the optical energy emanating from thefirst input fiber 12 into a beam 17. The collimated beam 17 impingesupon the filter 101, where λ₁ . . . λ_(n)-λ_(m) is reflected and focusedby the lens 16 to the output fiber 20.

[0065] Simultaneously, λ_(m) is transmitted through the filter 101 intothe first refracting element 44. By virtue of the physical phenomenon oftotal internal reflection, the collimated beam 17 containing λ_(m) isreflected off of the first reflecting surface into a second collimatinglens 22. The second collimating lens 22 focuses the collimated beam 17containing λ_(m) onto a second output (drop) fiber 26 that terminates ata focal plane of the second collimating lens 22. The second output fiber20 serves as a drop for the optical energy of λ_(m). By this process,λ_(m) has been dropped from λ₁ . . . λ_(n) the first output fiber 20 tothe second output (drop) fiber 26.

[0066] Opposing optical energy, the add channel containing λ_(m)′ isintroduced at a second input (add) fiber 24 terminating at the focalplane of the second collimating lens 22. The second collimating lenscollimates the optical energy emanating from the second input (add)fiber 24 into a beam 28. The collimated beam 28 is reflected off of thefirst reflecting surface 33 into the filter 101. The filter 101 reflectsall wavelengths other than λ_(m)′ back to the fiber 26. Filter 101simultaneously transmits λ_(m)′ to the first collimating lens 16, which,in turn, focuses the energy onto the first output fiber 20. The firstoutput fiber 20 serves as a sink for the optical energy. By thisprocess, the optical energy λ₁ . . . λ_(n) has been transferred from thefirst input fiber 12 to the first output fiber 20 and has dropped λ_(m)at the drop fiber 26 and added λ_(m)′ from the add fiber 24. Thisresults in λ₁ . . . λ_(n)-λ_(m)+λ_(m)′ at the output fiber 20.

[0067] Now FIG. 10 will be described assuming that the FTIR reversingswitch 50 is in a closed state, the air gap 35 being perhaps on theorder of {fraction (1/10)}^(th) of a wavelength in thickness. The firstinput fiber 12 provides a source of optical energy containing multiplewavelengths λ₁ . . . λ_(n) and terminates at the focal plane of thecollimating lens 16. The collimating lens 16 collimates the opticalenergy emanating from the first input fiber 12 into a beam 17. Thecollimated beam 17 impinges upon filter 101, where λ₁ . . . λ_(n)-λ_(m)is reflected and focused by lens 16 to output fiber 20.

[0068] Simultaneously, λ_(m) is transmitted into the first refractingelement 44. The air gap 35 having substantially closed and thereflection of the first reflecting surface 33 having been frustrated,the collimated beam 17 passes through the interface defined by the firstreflecting surface 33 and the frustrating surface 42 of the frustratingrefracting body 40. The collimated beam 17 then impinges upon and isreflected from an angled mirror 38 formed within or on the frustratingrefracting body 40. The collimated beam 17 then passes back through theinterface defined by the first reflecting surface 33 and the frustratingsurface 42 and returns to the filter 101 and then to the firstcollimating lens 16. The first collimating lens 16 focuses the opticalenergy onto the first output fiber 20. By this process, the opticalenergy containing multiple wavelengths λ₁ . . . λ_(n) has beentransferred from the first input fiber 12 to the first output fiber 20,without adding λ_(m)′ or dropping λ_(m).

[0069] In like fashion, the second input (add) fiber 24 provides anopposing source of optical energy λ_(m)′ and terminates at the focalplane of the second collimating lens 22 that collimates the opticalenergy emanating from the second input fiber 24 into the collimated beam28.

[0070] The air gap 35 again having substantially closed and thereflection of the first reflecting surface 33 frustrated, the collimatedbeam 28 passes through the interface defined by the first reflectingsurface 33 and the frustrating surface 42 of the frustrating refractingbody 40. The collimated beam 28 then impinges upon and is reflected fromthe angled mirror 38. The collimated beam 28 then passes back throughthe interface defined by the first reflecting surface 33 and thefrustrating surface 42 and returns to the second collimating lens 22.The first collimating lens 22 focuses the optical energy λ_(m)′ onto thesecond output (drop) fiber 26. By this process, the optical energyλ_(m)′ has been transferred from the second input (add) fiber 24 to thesecond output (drop) fiber 26.

[0071] It will be recognized by those skilled in the art that λ_(m) andλ_(m)′ can be replaced by a series of wavelengths λ₁ . . . λ_(n) and λ₁′. . . λ_(n)′ and that the filters can be bandpass, comb, longpass orshortpass filters. It is therefore apparent that the present inventionprovides a means of remotely configuring an add and drop filter suchthat λ_(m) is dropped and λ_(m)′ is added or, alternatively, nothing isadded or dropped.

[0072] Those skilled in the art will readily see that the fibers 12, 20can be interchanged as the input and output fibers (requiring, ofcourse, the fibers 24, 26 to be interchanged as the add and dropfibers). Alternatively, the fibers 24, 26 could function as the inputand output fibers (in which case the fibers 12, 20 would be the add anddrop fibers).

[0073] Turning now to FIG. 11, illustrated is a four channel integratedadd/drop multiplexer generally designated 130 and constructed accordingto the principles of the present invention. The four channel integratedadd/drop multiplexer 130 is built about a refracting element 103 andprovides optical filters 101 b, 101 c, 101 d, 101 e between thecollimating lens 16 and the first refracting element 44 of the FTIRreversing optical switches 50 b, 50 c, 50 d, 50 e. FIG. 11 will beinitially described assuming that the FTIR reversing switch 50 b is inan open state, the air gap 35 being perhaps on the order of onewavelength in thickness.

[0074] The first input fiber 12 provides a source of optical energycontaining multiple wavelengths λ₁ . . . λ_(n) and terminates at thefocal plane of the collimating lens 16. The collimating lens 16collimates the optical energy emanating from the first input fiber 12into a beam 17 a. The collimated beam 17 a impinges upon the filter 101b, where the collimated beam 17 b containing λ₁ . . . λ_(n)-λ_(b) isreflected to the filter 101 c. Simultaneously λ_(b) is transmitted intothe refracting element 44. By virtue of the physical phenomenon of totalinternal reflection, the collimated beam 17 a containing λ_(b) isreflected off of the first reflecting surface into a second collimatinglens 22 b. The second collimating lens 22 b focuses the collimated beam17 containing λ_(b) onto a second output (drop) fiber 26 b thatterminates at a focal plane of the second collimating lens 22. Thesecond output fiber 20 b serves as a drop for the optical energy ofλ_(b). By this process, λ_(b) has been dropped from λ₁ . . . λ_(n) thefirst output fiber 20 to the second output (drop) fiber 26.

[0075] The add channel, containing λ_(b)′, is introduced at a secondinput (add) fiber 24 b terminating at the focal plane of the secondcollimating lens 22 b. The second collimating lens collimates theoptical energy emanating from the second input (add) fiber 24 into abeam 28. The collimated beam 28 is reflected off of the first reflectingsurface 33 into the filter 101. The filter 101 reflects all wavelengthsother than λ_(b)′ back to the fiber 26. The filter 101 simultaneouslytransmits λ_(b)′ to first collimating lens 16, which, in turn, focusesthe energy into the first output fiber 20.

[0076] Now FIG. 11 will be described assuming that the FTIR reversingswitch 50 b is in a closed state, the air gap 35 being perhaps on theorder of {fraction (1/10)}^(th) of a wavelength in thickness. The firstinput fiber 12 provides a source of optical energy containing multiplewavelengths λ₁ . . . λ_(n) and terminates at the focal plane of thecollimating lens 16. The collimating lens 16 collimates the opticalenergy emanating from the first input fiber 12 into a beam 17 a. Thecollimated beam 17 a containing λ₁ . . . λ_(n) impinges upon filter 101b, where λ₁ . . . λ_(n)-λ_(b) is reflected to filter 101 c.Simultaneously λ_(b) is transmitted into the first refracting element44. The air gap 35 having substantially closed and the reflection of thefirst reflecting surface 33 having been frustrated, the collimated beam17 passes through the interface defined by the first reflecting surface33 and the frustrating surface 42 of the frustrating refracting body 40.The collimated beam 17 then impinges upon and is reflected from anangled mirror 38 formed within or on the frustrating refracting body 40.The collimated beam 17 then passes back through the interface defined bythe first reflecting surface 33 and the frustrating surface 42 andreturns to the filter 101 and then to the first collimating lens 16. Thefirst collimating lens 16 focuses the optical energy into the firstoutput fiber 20.

[0077] In like fashion, the second input (add) fiber 24 provides anopposing source of optical energy λ_(b)′ and terminates at the focalplane of the second collimating lens 22 that collimates the opticalenergy emanating from the second input fiber 24 into the collimated beam28 b.

[0078] The air gap 35 again having substantially closed and thereflection of the first reflecting surface 33 frustrated, the collimatedbeam 28 b passes through the interface defined by the first reflectingsurface 33 b and the frustrating surface 42 b of the frustratingrefracting body 40. The collimated beam 28 b then impinges upon and isreflected from the angled mirror 38 b. The collimated beam 28 b thenpasses back through the interface defined by the first reflectingsurface 33 b and the frustrating surface 42 b and returns to the secondcollimating lens 22 b. The second collimating lens 22 b focuses theoptical energy λ_(m)′ onto the second output (drop) fiber 26 b. By thisprocess, the optical energy λ_(b)′ has been transferred from the secondinput (add) fiber 24 b to the second output (drop) fiber 26 b. Theprocess described above is repeated in the same manner at the switch 50c, the filter 101 c, the switch 50 d, the filter 101 d, the switch 50 eand the filter 101 e with λ_(c)′, λ_(d)′ and λ_(e)′ being added andλ_(c), λ_(d) and λ_(e) being dropped at filters 101 c, 101 d, 101 erespectively.

[0079] One skilled in the pertinent art will recognize that this processcan be repeated with additional filters and switches. He will alsorecognize that a last filter 101 m can be replaced with a mirror toreturn any remaining wavelengths to the output fiber 20, that λ′ can bereplaced by a series of wavelengths λ₁′ . . . λ_(n)′ and that thefilters can be bandpass, comb, longpass or shortpass filters.

[0080] It is therefore apparent that the present invention provides ameans to remotely configure an add and drop filter such that λ_(b),λ_(c), λ_(d) and λ_(e) are dropped and λ_(b)′, λ_(c)′, λ_(d)′ and λ_(e)′are added or, in the alternative, that any combination of wavelengthscan be selectively added or dropped.

[0081] Turning now to FIG. 12, illustrated is a cascaded single channelintegrated optical add/drop multiplexer that includes first and secondadd/drops designated 120 a, 120 b, respectively, constructed accordingto the principles of the present invention. Each individual add/drop 120a, 120 b has been described above. The add/drop 120 a selectively addsλ_(m)′ and drops λ_(m). By cascading the add/drop 120 b with theadd/drop 120 a, the add/drop 120 b thereafter selectively adds λ₁′ anddrops λ₁. Those skilled in the art will readily see that λ′ can bereplaced by a series of wavelengths λ₁′ . . . λ_(n)′ and that thefilters can be bandpass, comb, longpass or shortpass filters.

[0082] It is thus apparent that the present invention provides a meansto remotely configure an add and drop filter such that λ₁ and λ_(m) aredropped and λ₁′ and λ_(m)′ are added. Alternatively, nothing is added ordropped, or any combination of wavelengths is added or dropped. Thoseskilled in the pertinent art will also recognize that any number ofadd/drops 120 can be cascaded to provide the option of adding anddropping any number of wavelengths λ_(m). It should also be apparentthat the multiplexer can be alternatively constructed in a hierarchicalfashion, wherein bands of wavelengths are successively subdivided intochannels by successive add/drops arranged as are branches in a tree.

[0083] From the above, it is apparent that the present inventionintroduces novel architectures of integrated optical add/drop wavelengthdivision multiplexers and FTIR switches. In one embodiment, an add/dropincludes: (1) a primary refracting body having a total internalreflecting surface and capable of transmitting optical energytherethrough, (2) a frustrating refracting body having a frustratingsurface located proximate the total internal reflecting surface, (3) anactuator, coupled to the primary refracting body and the frustratingrefracting body, that drives at least a center portion of thefrustrating refracting body thereby to frustrate a reflection of thetotal internal reflecting surface and (4) an optical filter, opticallyaligned with the primary refracting body, that configurably passesselected wavelengths of light through the primary refracting body andreflects remaining wavelengths.

[0084] Although the present invention has been described in detail,those skilled in the art should understand that they can make variouschanges, substitutions and alterations herein without departing from thespirit and scope of the invention in its broadest form.

What is claimed is:
 1. A remotely configurable add/drop for a WDMoptical network, comprising: a primary refracting body having a totalinternal reflecting surface and capable of transmitting optical energytherethrough; a frustrating refracting body having a frustrating surfacelocated proximate said total internal reflecting surface; an actuator,coupled to said primary refracting body and said frustrating refractingbody, that drives said frustrating refracting body thereby to frustratea reflection of said total internal reflecting surface; and an opticalfilter, optically aligned with said primary refracting body, thatconfigurably passes selected wavelengths of light through said primaryrefracting body and reflects remaining wavelengths.
 2. The add/drop asrecited in claim 1 wherein said optical filter is coupled to saidprimary refracting body.
 3. The add/drop as recited in claim 1 whereinsaid optical filter is composed of a dielectric material.
 4. Theadd/drop as recited in claim 1 wherein said primary refracting body iscomposed of glass.
 5. The add/drop as recited in claim 1 wherein saidfrustrating refracting body is composed of glass.
 6. The add/drop asrecited in claim 1 wherein said actuator is composed of a piezoelectricbimorph.
 7. The add/drop as recited in claim 1 further comprising: afirst collimating lens optically aligned with said optical filter; and afirst input fiber and a first output fiber coupled to said firstcollimating lens.
 8. The add/drop as recited in claim 1 furthercomprising: a first collimating lens optically aligned with a surface ofsaid optical filter; a second collimating lens coupled to a surface ofsaid main refractive body; a first input fiber and a first output fibercoupled to said first collimating lens; and a second input fiber and asecond output fiber coupled to said second collimating lens.
 9. Theadd/drop as recited in claim 1 wherein said actuator drives said atleast said center portion of said frustrating refracting body to aposition that only partially frustrates said reflection of said totalinternal reflecting surface.
 10. The add/drop as recited in claim 1wherein said frustrating refracting body comprises a mirror.
 11. Aremotely configurable add/drop for a WDM optical network, comprising: aprimary refracting body having a total internal reflecting surface andcapable of transmitting optical energy therethrough; an optical filter,optically aligned with a first surface of said primary refracting body,that configurably passes selected wavelengths of light through saidprimary refracting body and reflects remaining wavelengths; a firstcollimating lens optically aligned with a surface of said opticalfilter; a second collimating lenses coupled to a second surface of saidprimary refracting body; a frustrating refracting body located proximatesaid total internal reflecting surface and having a mirror; and anactuator, coupled to said primary refracting body and said frustratingrefracting body, that drives said frustrating refracting body between anopen state, in which said add/drop processes said selected wavelengths,and a closed state, in which said add/drop leaves said selectedwavelengths substantially intact.
 12. The add/drop as recited in claim11 wherein said optical filter is coupled to said primary refractingbody.
 13. The add/drop as recited in claim 11 wherein said opticalfilter is composed of a dielectric material.
 14. The add/drop as recitedin claim 11 wherein said actuator drives said frustrating refractingbody from said open state to said closed state.
 15. The add/drop asrecited in claim 11 further comprising: a first input fiber and a firstoutput fiber coupled to said first collimating lens; and a second inputfiber and a second output fiber coupled to said second collimating lens.16. The add/drop as recited in claim 11 wherein said primary refractingbody is composed of glass.
 17. The add/drop as recited in claim 11wherein said frustrating refracting body is composed of glass.
 18. Theadd/drop as recited in claim 11 wherein said actuator is composed of apiezoelectric bimorph.
 19. The add/drop as recited in claim 11 whereinsaid mirror is composed of enhanced silver.
 20. The add/drop as recitedin claim 11 wherein said actuator drives said frustrating refractingbody to an intermediate state in which a collimated beam emanating fromsaid first collimating lens partially reflects off said total internalreflecting surface and travels toward said second collimating lens andpartially reflects off said mirror and travels back toward said firstcollimating lens.
 21. An integrated channel add/drop multiplexer,comprising: a cascaded plurality of interconnected remotely configurableadd/drops, each of said add/drops including: a primary refracting bodyhaving a total internal reflecting surface and capable of transmittingoptical energy therethrough, a frustrating refracting body having afrustrating surface located proximate said total internal reflectingsurface, an actuator, coupled to said primary refracting body and saidfrustrating refracting body, that drives said frustrating refractingbody thereby to frustrate a reflection of said total internal reflectingsurface, and an optical filter, optically aligned with said primaryrefracting body, that configurably passes selected wavelengths of lightthrough said primary refracting body and reflects remaining wavelengths.22. The multiplexer as recited in claim 21 wherein each of saidadd/drops configurably passes separate selected wavelengths.
 23. Themultiplexer as recited in claim 21 wherein said optical filter iscoupled to said primary refracting body.
 24. The multiplexer as recitedin claim 21 wherein said primary retracting body is composed of glass.25. The multiplexer as recited in claim 21 wherein said frustratingrefracting body is composed of glass.
 26. The multiplexer as recited inclaim 21 wherein said actuator is composed of a piezoelectric bimorph.27. The multiplexer as recited in claim 21 further comprising: a firstcollimating lens optically aligned with said optical filter; and a firstinput fiber and a first output fiber coupled to said first collimatinglens.
 28. The multiplexer as recited in claim 21 further comprising: afirst collimating lens optically aligned with said optical filter; asecond collimating lens coupled to a surface of said main refractivebody; a first input fiber and a first output fiber coupled to said firstcollimating lens; and a second input fiber and a second output fibercoupled to said second collimating lens.
 29. The multiplexer as recitedin claim 21 wherein said actuator drives said at least said centerportion of said frustrating refracting body to a position that onlypartially frustrates said reflection of said total internal reflectingsurface.
 30. The multiplexer as recited in claim 21 wherein saidfrustrating refracting body comprises a mirror.